1. Field of Invention
The present invention relates to a method of current detection. More particularly, the present invention relates to a method and a device for computing the root-mean-square value of a wave function by sampling the wave function and processing the sampled signals digitally.
2. Description of Related Art
Allowable current and maximum current for the normal operation of a pick-up head system in an optical storage device are normally specified. The optical storage device is for example a CD-ROM device, a CD-R/RW device, a DVD-compatible device. For instance, for model SF-HD2S CD-ROM produced by Sanyo, the allowable current I1 for continuous current is 120 mA rms and the maximum current I2 for a two-second interval cannot exceed 240 mA rms. To prevent unwanted failure of pick-up head due to excess current, a circuit capable of detecting current flow to the pick-up head must be provided. When a current in excess of the maximum allowable current I1, and the maximum current I2 is detected, immediate cutting of current going to the pick-up head is preferred.
The value of the allowable current and the maximum current specified for a particular type of pick-up head is normally in a root-mean-square type. However, a conventional current monitor for a pick-up head normally measures only its DC value. For example, when a wave function is passed into a low-pass filter, the DC value of the wave function is output from the low-pass filter. Hence, a low-pass filter is able to monitor the DC current flowing into the pick-up head. If the measured DC current exceeds a maximum allowable value, current going to the pick-up head can be shut off.
However, DC current and root-mean-square current are two different types of current measurements. It is possible to have a value obtained from a root-mean-square measurement to exceed the maximum allowable current while the value obtained from a DC measurement is still below the maximum. Consequently, the pick-up head may function abnormally leading to a shorter life or premature failure.